1. Field of the Invention
The present invention relates to power control. More particularly, the present invention relates to a method and apparatus for determining a transmission location of a power control command based on an UpLink (UL) control channel and for performing power control in a broadband wireless communication system.
2. Description of the Related Art
In a next generation communication system, intensive research is being conducted to provide users with high-speed services having various Qualities of Service (QoSs). Power control schemes used in communication systems may be classified as open-loop power control schemes and closed-loop power control schemes according to whether a Base Station (BS) receives feedback information from a Mobile Station (MS).
The open-loop power control schemes are schemes in which a transmitter for performing power control independently determines a channel state of a receiver and performs the power control. The open-loop power control schemes control power based on reversibility between UpLink (UL) and DownLink (DL) channels. Here, the reversibility between the UL and DL channels means that MSs having the same location with respect to a BS experience similar path attenuation due to a path attenuation based on a distance from the BS determining a channel quality, an antenna gain based on an antenna pattern, a shadowing effect by a topographic feature, multi-path fading, and the like. That is, the open-loop power control schemes are schemes in which, based on the reversibility between the DL and UL channels, a transmitter directly estimates a signal reception quality of a receiver, determines necessary transmit power, and transmits signals.
Unlike the open-loop power control schemes, the closed-loop power control schemes are schemes in which a transmitter controls transmit power as much as needed based on a signal reception quality of a receiver received over a feedback channel, without independently determining a channel quality. The closed-loop power control schemes have a disadvantage in which an overhead for the feedback channel occurs. However, there is an advantage in that, because the transmitter may be aware of a channel quality at the receiver, the closed-loop power control schemes may accurately control magnitudes of transmit signals compared to the open-loop power control schemes.
For instance, legacy Orthogonal Frequency Division Multiple Access (OFDMA) broadband wireless communication systems (e.g., the Institute of Electrical and Electronics Engineers (IEEE) standard 802.16 systems) may transmit Transmit Power Control (TPC) commands for all users using Information Element (IE) formats or MS identifiers, but overheads for feedback channels are large.
As described above, the closed-loop power control scheme has a problem because, as the number of MSs provided with communication services from a BS in a broadband wireless communication system increases, an amount of channel quality information that the BS should receive from each MS over a feedback channel increases and, in addition, an overhead of a feedback channel assigned for receiving the channel quality information increases.
Therefore, there exists a need for a method and apparatus of efficient power control command transmission for closed-loop power control at the time of UL power control in a wireless communication system.